Conventionally, a circularly polarizing plate has been provided to an organic electroluminescent display device (hereinafter, may be appropriately referred to as an “organic EL display device”) for reducing reflection of outside light on a display surface in some cases. In general, a film obtained by combining a polarizing film and a λ/4 plate is used as such a circularly polarizing plate. However, most of conventional λ/4 plates were capable of actually achieving a phase difference of an approximately quarter wavelength only with light in a specific narrow wavelength range. Therefore, although reflection of outside light in a specific narrow wavelength range can be reduced by the circularly polarizing plate, reduction of reflection of other outside light was insufficient.
To deal with this, a broadband λ/4 plate obtained by combining a λ/4 plate and a λ/2 plate has been recently proposed (see Patent Literatures 1 to 6).